The present invention relates generally to semiconductor thermal processing systems, and more specifically to a system and method for rapid thermal processing using a linearly-moving heating assembly with a radially-tunable thermal radiation profile.
High temperature processing of semiconductor (e.g., silicon) wafers is important for manufacturing modern microelectronics devices. Such processes, including silicide formation, implant anneal, oxidation, nitridation, diffusion drive-in, chemical vapor deposition (CVD) and atomic layer deposition (ALD), may be performed at high temperatures and in proper ambient gases or vacuum using conventional thermal processing techniques. Furthermore, many modern microelectronics circuits require feature sizes smaller than one micron and junction depths less than a few hundred angstroms. In order to limit both the lateral and downward diffusion of dopants, as well as to provide a greater degree of control during processing, it is desirable to minimize the duration of high temperature processing as well as vary the gaseous composition around the semiconductor wafers.
One approach for minimizing processing time utilizes a single-wafer rapid thermal processor (RTP). Single-wafer rapid thermal processing of semiconductor wafers provides a powerful and versatile technique for fabrication of ultra-large-scale-integrated (ULSI) electronic devices. Conventional systems and methods of wafer thermal processing may suffer from various shortcomings, however, as will be described hereafter.
One conventional RTP system combines low thermal mass photon-assisted rapid thermal heating with an inert or reactive gaseous ambient for semiconductor wafer processing. Such a single-wafer RTP system utilizes high intensity lamps, optical temperature sensors and sophisticated control algorithms to heat a semiconductor wafer at a high temperature ramp rate, thereby reducing problems associated with high thermal budget to device fabrication. In lamp-based processing, the wafer is generally heated to temperatures of between 450xc2x0 C. to 1400xc2x0 C. and may furthermore be rapidly cooled after processing. Problems may be encountered, however, with the use of high intensity lamps as a heat source, particularly for larger diameter wafers. Specifically, it may be difficult to maintain a uniform temperature across a wafer due to individual lamp spacing, as well as other factors.
Typically, not only do temperature differences arise during heating and cooling transients in lamp-based RTP systems, but non-uniformities may also persist during processing. As illustrated in prior art FIG. 1A, a conventional lamp-based RTP lamp assembly 10 is shown, wherein the lamp assembly comprises a plurality of individual incandescent lamps 20. The plurality of lamps 20 are distributed across a surface 15 of the lamp assembly 10, leaving physical spaces 30 between each individual lamp. FIG. 1B illustrates a partial cross-section of the lamp assembly 10, illustrating several individual lamps 20. Each lamp 20 comprises a filament 40, such as tungsten, whereby electrical current passing through the filament resistively heats the filament, thus emitting thermal radiation 50 outward from the lamp. However, a filament 40 only takes a very small portion of physical space in a lamp 20. The spaces 30 between lamps 20 as well as the largely empty spaces inside lamps 20, however, contribute to the non-uniformity of the received thermal radiation over the substrate 60. To obtain uniform heating, lamp based systems typically utilize some combination of optical guides, lenses, and/or reflectors (not shown), as well as wafer rotation, to more evenly distribute thermal radiation onto the substrate 60. Despite these measures, it may be necessary in some systems to actively switch individual lamps or groups of lamps on and off rapidly to control the wafer temperature and minimize the effects of the non-uniform thermal radiation from the lamps. Furthermore, additional problems may be encountered in lamp-based systems due to aging and degradation of lamps and other components. As a result, it may be difficult to maintain repeatable performance, and a frequent replacement of parts and system cleaning may be necessary. Similar problems also exist in linear-lamp based rapid thermal processing systems.
Furthermore, since effective cooling of lamps is essential to increase the life time of lamps, the interior walls of a typical lamp-based RTP system are usually much colder than the wafer under processing and are not uniform in temperature. Therefore, heat transfer between the wafer and the interior walls via conduction and convection has detrimental effects to the uniform heating of the wafer under processing. Furthermore, ambient gases and gas-surface reaction products may deposit and condense onto the cold chamber walls of lamp-based RTP systems, blocking thermal radiation from lamps to the wafer and interfering with pyrometric temperature measurement.
A more advanced hot-wall rapid thermal processing (RTP) furnace (e.g., U.S. Pat. No. 4,857,689 and No. 6,183,127) can yield superior results over the lamp-based RTP systems in terms of temperature uniformity, process reproducibility and cost while still possessing comparable performance in terms of thermal budget and process throughput. In such hot-wall RTP systems, a stable monotonic temperature and thermal radiation gradient is maintained along the axis of the RTP furnace by constantly heating the upper section of the process chamber and actively cooling the lower section of the process chamber. This steady-state temperature profile is also axially symmetric, with a radial component optimized to ensure the uniform heating of a wafer.
The temperature of a wafer under processing is controlled by varying the position of the wafer along the temperature gradient. Since a thermal steady-state is maintained throughout the entire furnace, and between the furnace and the gas ambient, wafer heating is dominated by the thermal equilibration between the wafer and its furnace environment. Ambient gases flow through the hot wall chamber to interact with the wafer under processing. A hot-wall RTP furnace has a much larger total thermal radiation area than the total filament area of a lamp-based RTP system. A shortcoming associated with the hot-wall RTP systems is the relatively large internal volume of the process chamber, particularly when fast ambient gas switching is required during rapid thermal processing. However, fast ambient gas switching has been successfully realized by placing a wafer inside a small volume quartz reactor that linearly moves along the temperature gradient inside the process chamber.
Yet another rapid thermal processing system utilizes a heated block, or receptor, for thermally processing a wafer within a single chamber. The receptor resides in the chamber, and is heated by one or more resistive heaters. The wafer is inserted into the chamber and is placed on pins protruding through the receptor, and is subsequently lowered via the pins onto the receptor, such that heat transfer occurs from the receptor to the wafer via conduction, convection and radiation. The use of a receptor within a single chamber, however, may introduce various problems. For instance, in rapid thermal chemical vapor deposition (RTCVD) and low-pressure chemical vapor deposition (LPCVD) applications, the receptor can be coated by the material being deposited on the wafer (e.g., doped or undoped polysilicon, silicon dioxide, silicon nitride, etc.). The unwanted depositions on the receptor can result in particulate generation, cross contamination, process uniformity drifts, as well as problems associated with temperature measurement and process control.
Therefore, for at least the above mentioned reasons, an improved rapid thermal processing system and method is needed to alleviate many of the problems associated with the prior art.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention is directed to a semiconductor thermal processing system and a method for thermally processing a semiconductor wafer or substrate. The thermal processing system is operable to heat a substrate in vacuum or various gases to achieve desired physical and chemical changes for semiconductor device fabrication in an innovative manner to ensure improved thermal processing performance of a substrate.
According to one aspect of the present invention, a semiconductor thermal processing system and associated method is disclosed which provides a heater chamber and a process chamber, wherein the heater chamber and process chamber are environmentally isolated from one another by a thermally-transparent plate. The thermally transparent plate is generally transmissive to thermal radiation. A heater assembly comprising one or more quasi-continuous heater elements is situated in the heater chamber, whereby a linear translation assembly is operable to linearly move the heater assembly in a direction generally perpendicular to the wafer in the process chamber. A power supply is operable to provide heating current to the one or more heater elements, thereby emitting thermal radiation through the thermally-transparent plate toward a substrate situated within the process chamber.
According to another exemplary aspect of the present invention, one or more temperature sensors are operable to measure one or more temperatures associated with one or more respective locations on the substrate. A controller operably coupled to the heater assembly, linear translation assembly, and the one or more temperature sensors is operable to control the thermal radiation emitted by the one or more heater elements, as well as a distance between the heater assembly and the substrate. The control is based, at least in part, on the one or more measured temperatures.
According to yet another exemplary aspect of the present invention, the one or more heater elements comprise one or more heater rings, wherein the thermal radiation emitted by each of the one or more heater rings is individually adjustable, thereby making the heater assembly radially-tunable. A distance between each of the one or more heater rings and the substrate is furthermore adjustable, wherein the one or more heater rings can be situated in a common plane, or at varying distances from the substrate.
According to still another aspect of the invention, the linear motion of the heater assembly is primarily used to control the overall heating level, namely the temperature of a substrate (e.g., a silicon wafer) in the process chamber. The temperatures of the one or more heater rings are adjusted or tuned independently to control the thermal radiation power emitted by the one of more heater rings in order to tune the radial thermal radiation profile of the heater assembly and achieve the uniform heating across the substrate. One or a plurality of the heater rings can tilt independently with respect to the normal direction of the substrate for further tuning of thermal radiation profile of the heater assembly.
According to still another exemplary aspect of the invention, the thermal processing system can be operated under the control of an automation network comprising (1) sensors for temperature, position and pressure monitoring, (2) signal processing electronic circuitry and computer with proper algorithm or modeling software, and (3) electrical, mechanical and pneumatic driving units or controllers for the linear motion of the heater assembly and the heating powers to the one or more heater rings. The control network is operable to control the thermal radiation emitted by the heater assembly based on both the desired processing temperature and duration and the one or more measured temperatures from the substrate. The thermal radiation power of the heater assembly is controlled by varying the voltage or current delivered to the one or more heater rings from the power supplies. The total amount of thermal radiation received by the substrate under processing is controlled by adjusting the distance between the heater assembly and the substrate through the linear motion of the heater assembly. The control network is operable to control the composition, pressure, duration and switching of the ambient gas around the substrate in synchronization with the temperature versus time profile of the substrate.
To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.